You would need a very perfect and flexible CI system in place that wouldn't need to rebuild anything it doesn't need and only run the tests you want or only rec

You would need a very perfect and flexible CI system in place that wouldn't need to rebuild anything it doesn't need and only run the tests you want or only recently failed tests etc. Many CI systems would spin up a new box instead of using persistent so likely have to rebuild if no cache, etc. So basically I would say most of the overhead is in not having a persistent box with knowledge of last build or ability to choose what to run in there, which pretty much just equals to local capabilities.